Parallel Magnetic Circuit Motor

ABSTRACT

A parallel magnetic circuit motor includes a rotor without magnets and a stator with magnets. The stator has stator poles with windings. The windings are energized on a first plurality of stator poles with current in a same first direction and the windings are energized on a second plurality of stator poles with current in a same second direction opposite the same first direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/907,858, filed Oct. 19, 2010, entitled Parallel Magnetic CircuitMotor, which claims priority to U.S. Provisional Patent Application No.61/253,018, filed Oct. 19, 2009, entitled Parallel Magnetic CircuitMotor, the entire contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates generally to motors. More particularly, thisinvention is directed toward a parallel magnetic circuit motor.

BACKGROUND

It is desirable to optimize the magnetic circuit used in permanentmagnet [PM] machines to obtain the highest power density and efficiencypossible. Since PM machines typically have a relatively narrow highefficiency region on their fixed commutation (uncontrolled) torque vs.speed curve, many rotating machine technologists focus on increasing themotor size to power out ratio and the motor controller to enhance theoverall performance of PM machines.

The focus on the controller to enhance the performance of PM machines ispredicated on the belief that PM machines already operate at shearstress levels fairly close to their component materials' physicallimits. This statement is misleading, however, since the true limitingfactors are actually the permanent magnets and the geometry of themachine in which they are used, not the magnetically soft core materialsas implied.

Wound field machines such as series wound, switched or variablereluctance machines can operate at shear stress levels at the materiallimits. Since these machines use field coils, rather than permanentmagnets to produce the static magnetic field, the only limitation to themagnitude of the static field is the current carrying capacity of thecopper wire. Such machines can reach the physical limits of themagnetically soft core material and produce high gap flux densities, butalso result in increased I²R losses in the wound field coils and anincrease in weight due to the field coils.

Permanent magnets are used in rotating machines to replace the fieldcoils that produce static magnetic fields to provide three primarybenefits:

-   -   1) A reduction in the size of the machine since the magnets are        physically smaller than the coils they replace;    -   2) A reduction in the weight of the machine since the magnets        are physically lighter than the coils they replace; and    -   3) The elimination of the I²R losses attributed to the field        coils, thus reducing heat losses and therefore improving the        overall machine efficiency.

However, replacing a rotating machine's field coils with permanentmagnets has the following trade-offs/limitations:

-   -   1) The energy product of a permanent magnet is fixed, thereby        limiting the controllability of the static magnetic field;    -   2) State of the art permanent magnets cannot achieve the gap        flux densities that can be achieved with wound field coils;    -   3) Permanent magnets do not make good structural components and        can create bonding issues when placed on a machine's rotor;    -   4) Permanent magnets are more sensitive to temperature; and    -   5) The gap flux density is determined by the energy product of        the permanent magnet and will always be less than B_(r) or        approximately 1.25 Tesla for neodymium magnets with a typical        gap flux density of 0.8-˜1 Tesla with no power in the phase        coils. The field intensity [H] of the phase coils will drive the        gap density higher but cannot exceed ˜Br of the permanent        magnets. If the flux in the air gap coupling a permanent magnet        and a phase coil exceeds B_(r), the amount greater than B_(r)        will be primarily uncontrolled fringing flux. The permanent        magnet's domains between B_(r) and B_(max) require a greater        amount of energy to bring them into temporary magnetic        alignment.

This is not meant to diminish the importance of the motor controller forimproving performance but rather to state that mathematically,analytically and empirically it can be shown that the current andcommonly accepted PM machine geometries cannot achieve the shear stresslevels of wound field machines. The typical PM geometry is based on theconcept of simply replacing a wound field coil with a PM without fullyrealizing or accepting the limitations and consequences of such asimplistic approach. Therefore, it would be desirable to provide animproved PM circuit motor.

SUMMARY

A parallel magnetic circuit motor has a rotor without magnets and astator with magnets. Stator segments have windings. The rotor, statorand windings are configured to produce unidirectional current and torquewith electrically independent phases.

The disclosed Parallel Magnetic Circuit [PMC] or Parallel Path MagneticTechnology [PPMT] geometry provides solutions for many of thelimitations imposed by merely replacing a machine's wound field coilswith permanent magnets. Improvements include:

-   -   Increased power density by producing gap flux densities equal to        those of a field wound motor;    -   Increased efficiency by maintaining the I²R loss reduction and        weight benefits for using permanent magnets rather than wound        field coils;    -   Increased efficiency and reliability from the ability to        redirect the static field of a permanent magnet without applying        a destructive opposing field; and    -   Increased reliability from negating issues associated with        attaching or bonding permanent magnets to a rotating machine's        rotor.

Notable improved performance attributes include intrinsic higherefficiency over a wider operating range, a rectangular power outputcurve, higher air gap flux densities which result in higher powerdensity and no rotor attached components. These performancecharacteristics make a PMC machine a vastly superior solution comparedto several incumbent PM machine designs. However, in order for a PMC PMmachine to successfully compete with a greater share of incumbentsolutions, multiphase machine geometries need to be identified thatcould apply the PMC theory of operation.

In one aspect, a machine has a rotor without magnets and a statorcomprising a plurality of phase sections, each phase sectioncorresponding to one of a plurality of electrically independent phasesof the machine and each phase section having pairs of pole faces ofpermanent magnets arranged with same facing magnetic poles in which amagnetic pole of a permanent magnet faces a same magnetic pole ofanother permanent magnet, a plurality of stator poles between the samefacing permanent magnet pole faces, and a winding on each of the statorpoles.

In another aspect, a method comprises providing a machine comprising arotor without magnets and a stator comprising a plurality of phasesections, each phase section corresponding to one of a plurality ofelectrically independent phases of the machine and each phase sectionhaving pairs of pole faces of permanent magnets arranged with samefacing magnetic poles in which a magnetic pole of a permanent magnetfaces a same magnetic pole of another permanent magnet, a plurality ofstator poles between the same facing permanent magnet pole faces, and awinding on each of the stator poles.

In another aspect, a machine has a rotor without magnets and a statorcomprising a plurality of phase sections, each phase sectioncorresponding to one of a plurality of electrically independent phasesof the machine and each phase section having pairs of pole faces ofpermanent magnets arranged with same facing magnetic poles in which amagnetic pole of a permanent magnet faces a same magnetic pole ofanother permanent magnet, an even number of stator poles between thesame facing permanent magnet pole faces, and a winding on each of thestator poles.

In another aspect, a machine has a rotor without magnets and a statorcomprising a plurality of phase sections, each phase sectioncorresponding to one of a plurality of electrically independent phasesof the machine and each phase section having a plurality of northpermanent magnet pole faces arranged with north same facing magneticpoles, a plurality of south permanent magnet pole faces arranged withsouth same facing magnetic poles, a first plurality of stator polesbetween the north permanent magnet pole faces, a second plurality ofstator poles between the south permanent magnet pole faces, and awinding on each of the stator poles, wherein same facing magnetic polesare a magnetic pole of a permanent magnet facing a same magnetic pole ofanother permanent magnet.

In another aspect, a method comprises providing a rotor without magnetsfor a machine and providing a stator for the machine, the statorcomprising a plurality of phase sections, each phase sectioncorresponding to one of a plurality of electrically independent phasesof the machine and each phase section having pairs of pole faces ofpermanent magnets arranged with same facing magnetic poles in which amagnetic pole of a permanent magnet faces a same magnetic pole ofanother permanent magnet, an even number of stator poles between thesame facing permanent magnet pole faces, and a winding on each of thestator poles.

In another aspect, a method includes providing a rotor without magnetsfor a machine and providing a stator for the machine, the statorcomprising a plurality of phase sections, each phase sectioncorresponding to one of a plurality of electrically independent phasesof the machine and each phase section having a plurality of northpermanent magnet pole faces arranged with north same facing magneticpoles, a plurality of south permanent magnet pole faces arranged withsouth same facing magnetic poles, a first plurality of stator polesbetween the north permanent magnet pole faces, a second plurality ofstator poles between the south permanent magnet pole faces, and awinding on each of the first plurality of stator poles and secondplurality of stator poles, wherein same facing magnetic poles are amagnetic pole of a permanent magnet facing a same magnetic pole ofanother permanent magnet.

In another aspect, a method comprises in a machine comprising a rotorwithout magnets and a stator comprising a plurality of phase sections,each phase section corresponding to one of a plurality of electricallyindependent phases of the machine and each phase section having pairs ofpole faces of permanent magnets arranged with same facing magnetic polesin which a magnetic pole of a permanent magnet faces a same magneticpole of another permanent magnet, the pairs of pole faces comprising twonorth same facing permanent magnet pole faces and two south same facingpermanent magnet pole faces, the stator further comprising two statorpoles between the two north same facing permanent magnet pole faces andtwo other stator poles between the two south same facing permanentmagnet pole faces, and a winding on each of the stator poles, energizingthe windings on the two stator poles with current in a same firstdirection and energizing the windings on the two other stator poles withcurrent in a same second direction opposite the same first direction.

In another aspect, a method comprises in a machine comprising a rotorwithout magnets and a stator comprising a plurality of phase sections,each phase section corresponding to one of a plurality of electricallyindependent phases of the machine and each phase section having aplurality of north permanent magnet pole faces arranged with north samefacing magnetic poles, a plurality of south permanent magnet pole facesarranged with south same facing magnetic poles, a first plurality ofstator poles between the north permanent magnet pole faces, a secondplurality of stator poles between the south permanent magnet pole faces,and a winding on each of the stator poles, wherein same facing magneticpoles are a magnetic pole of a permanent magnet facing a same magneticpole of another permanent magnet, energizing the windings on the firstplurality of stator poles with current in a same first direction andenergizing the windings on the second plurality of stator poles withcurrent in a same second direction opposite the same first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is more fully appreciated in connection with the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 shows a simple magnetic circuit.

FIG. 2 shows graph of the attractive force between the poles and thepermanent magnet versus the phase coil current.

FIG. 3 shows flux from the permanent magnet, with no current in thephase coils, already permeates the magnetically soft core which createsan attracting force.

FIG. 4 shows a graph of the attracting and repelling force between thepoles and the permanent magnet versus the phase coil current.

FIG. 5 illustrates a three phase PM machine in accordance with anembodiment of the invention.

FIG. 6 illustrates flux densities for the machine of FIG. 8.

FIG. 7 shows the flux density in the air gap over 360 degrees.

FIG. 8 shows the flux densities as a rotor permanent magnet aligns witheach of the three phases.

FIG. 9 illustrates a phase one pole with phase 2 and 3 winding slotsremoved.

FIG. 10 shows the flux density for phase 1 if the winding slots forphases two and three are removed.

FIG. 11 shows the flux density in the air gap over 360 degrees for phaseone with the winding slots for phases two and three removed and the sameapplied current as was used to create FIG. 7.

FIG. 12 illustrates a design with higher air gap flux densities.

FIG. 13 illustrates rise time for phase coils as a function ofattracting and repelling a permanent magnet.

FIG. 14 shows a model for one phase of a motor as a series resistor,inductor and voltage source.

FIG. 15 shows a section of the rotor and stator that comprise a phasesection.

FIG. 16 shows a case where no phase coils are energized.

FIG. 17 shows how the flux from the permanent magnets adds and isdirected through a given set of stator poles by selectively energizingphase coils.

FIG. 18 illustrates magnetic polarities utilized in accordance with anembodiment of the invention.

FIG. 19 illustrates permanent magnet pole face adjustments utilized inaccordance with an embodiment of the invention.

FIG. 20 shows two uses of bidirectional current in a phase coil.

FIG. 21 illustrates stored energy dissipation in accordance with anembodiment of the invention.

FIG. 22 shows a PMC two phase machine geometry.

FIG. 23 contains the timing table for a PMC two phase machine by phaseand pole designators.

FIG. 24 shows a three phase PMC machine.

FIG. 25 shows the timing sequence of a three phase PMC machine.

FIG. 26 shows a six phase PMC machine.

FIG. 27 shows the timing sequence of a six phase PMC machine.

FIG. 28 shows a typical uncontrolled (left) and controlled (right) PMmotor curve.

FIG. 29 shows performance comparison versus market alternatives.

FIG. 30 is a speed vs. torque & watts out curve speed vs. torque curvefor a fixed commutation 6 phase 1 HP machine PMC geometry.

FIG. 31 shows the speed vs. torque curve for a fixed commutation 6 phase1 HP machine with PMC geometry.

FIG. 32 illustrates performance advantages achieved over conventionalmotors in accordance with an embodiment of the invention.

FIG. 33 shows a speed vs. torque and power out for a 10 KW motor.

FIG. 34 shows speed vs. torque and efficiency in accordance with anembodiment of the invention.

DETAILED DESCRIPTION

In order to understand the problems solved by the magnetic circuits orgeometries used in accordance with the invention (occasionally referredto as a QM Power PMC machine), the limitations associated with commonlyused PM machine geometries first needs to be examined. This sectionaddresses the principles (and shortcomings) of the commonly usedmagnetic circuit within non-PMC brush and brushless three Phase PMmotors.

Brushless three Phase PM motors use overlapped phase windings wound on amagnetically soft iron stator or rotor. During motor operation, thesephase windings produce magnetic fields that attract or repel permanentmagnets mounted on the rotor [brushless] or that comprise the stator[brush]. The overlapped phase windings also reduce the magnetically softiron forming a pole for a phase, since winding slots must be present inthat pole to accommodate the other phases.

A first limitation of commonly used PM machine geometries relates toattracting and repelling forces. In particular, the Maxwell stressintegral in the air gaps for the same amount of applied phase coilcurrent is different for an electromagnetic field that is repelling apermanent magnet than one attracting a permanent magnet.

The simple magnetic circuit of FIG. 1, is used to prove this statement.FIG. 1 illustrates permanent magnets, back iron, air gaps, poles andcoils. When a phase coil is energized in a manner to attract a permanentmagnet, the magnetic fields of the phase coil and permanent magnetcouple and the attractive force immediately begins to increase with themagnitude of the current in the phase coil. A graph of the attractiveforce between the poles and the permanent magnet versus the phase coilcurrent is in shown in FIG. 2.

Since flux from the permanent magnet, with no current in the phasecoils, already permeates the magnetically soft core, the attractingforce does not begin at zero.

When a phase coil is energized in a manner to repel a permanent magnet,the magnetic fields of the phase coil and permanent magnet oppose. Fluxfrom the permanent magnet, with no current in the phase coils, alreadypermeates the magnetically soft core which creates an attracting forceas shown in FIG. 3.

When current flows in the phase coil, the flux produced by the coil mustfirst oppose and displace the flux from the permanent magnets. As themagnitude of the phase coil current increases, producing a flux [L*i]that opposes the preexisting permanent magnet flux, the attracting forceis reduced but no repelling force is present until the preexistingpermanent magnet flux is first displaced.

A graph of the attracting and repelling force between the poles and thepermanent magnet versus the phase coil current is shown in FIG. 4. Thegraph begins at a nonzero attracting force for both cases, howeverrepelling forces are not present until the point where the force curvepasses through zero and produces negative values.

As can be seen in the graphs in FIGS. 2 and 4, at the maximum appliedphase coil current, a repelling force of just 36 lbs is created asopposed to 312 lbs for an attracting force at the same applied current.

The equations for calculating Maxwell stress are quadratic and implythat for the same applied phase current, the attracting and repellingmagnetic forces will remain at the same ratio no matter what sizemagnets arc used. The phase coil turns could be increased resulting inincreased resistance. This increased resistance requires a higher inputvoltage with a lower current [I=V/R] but the power [P=VI] remains thesame.

The above magnetic circuit is used to illustrate that the attracting andrepelling forces are not the same when identical current is applied tothe phase coils due to the fact that the permanent magnets produce aflux through the magnetically soft core material without current in thecoils. It further illustrates that when a phase coil is energized torepel a permanent magnet, the majority of the current is used todisplace the opposing permanent magnet flux rather than producing arepelling force or ‘pushing’ torque to move the rotor to the next pole.

FIG. 5 illustrates these principles when reduced to practice in anactual three phase PM machine.

Considering PH1, if the rotor is turning in a clockwise (CW) direction,with a permanent magnet aligned with the PH1 poles as shown, pole(s) Awould be applying an attracting force on a rotor magnet producing amajor contribution to torque, pole(s) C would be applying a repellingforce on a rotor magnet with a minor contribution to torque, and pole(s)B would have negligible or no contribution to torque. (Note that phase 1poles A, B, and C combine to form a single phase 1 pole since thismachine utilizes overlapped phases and winding slots for the otherphases, which must also be present in the phase 1 pole. Therefore, phase1 has 12 poles with each pole consisting of sub-poles A, B, and C.)

The three overlapped phases maintain this relationship as the rotorturns where a ‘leading’ pole is always attracting a rotor permanentmagnet and a ‘trailing’ pole is always repelling a rotor permanentmagnet, independent of rotational direction, and the central pole willhave little to no contribution to torque. For the other phases [PH1 poleA=PH2 pole B=PH3 pole C], [PH1 pole B=PH2 pole C=PH3 pole A] and [PH1pole C=PH2 pole A=PH3 pole B].

If phase 1 is energized to V_(peak) the flux densities for the machinein FIG. 5 are as shown in FIG. 6.

The maximum gap density at the pole tips for this machine geometry wouldbe approximately equal to B_(r) of the permanent magnet, with theintegral values for the entire PH1 pole significantly lower than B_(r).The ‘trailing’ or repelling poles cannot reach B_(r), as shown in FIG.6.

FIG. 7 shows the flux density in the air gap over 360 degrees. The 12attracting phase one poles can clearly be seen and, as suggested by thesimple magnetic circuit analysis in the first part of this section, thesignificant torque contribution is produced by the attracting fields;the repelling fields contribute very little when compared to the totaltorque. If one looks more closely at FIG. 6, it can be seen that theattracting field on the ‘leading’ end of a permanent magnet raises theload line to Br at the pole tips while the repelling fields on thetrailing end of the same permanent magnet are driven below ½ Br. Whilestrong opposing fields can be present using neodymium magnets owing totheir high coercive force, a PM machine that uses ceramic magnets to thephase current levels shown in FIG. 6 would eventually demagnetize thoseceramic magnets and render the system inoperable. That is why most PMmachines that use ceramic magnets give a current rating that cannot beexceeded so as to prevent destructive opposing fields from being appliedto the permanent magnets. Further, at any given angular position onlyabout 30% of the area of the rotor to stator gap interface contributesignificantly to the production of torque.

The gap flux densities shown in FIG. 7 are flux densities for phase one(of the three phases) when a permanent magnet is aligned with thatphase. FIG. 8 shows the flux densities as a rotor permanent magnetaligns with each of the three phases.

In summary, the torque delivered to the shaft will always be the sum ofthe repelling and attracting forces in a PM machine's air gap. Theattracting forces will always be dominant and the repelling forces willalways have a higher loss when compared to their current versus theforce produced.

Unless high coercive force permanent magnets are used, the phasecurrents must be limited to prevent demagnetization of the permanentmagnets.

It follows that only about 30% of the area of the rotor to stator airgap interface is utilized to produce the majority of the torque;specifically, the poles producing an attracting force for a three phasePM machine like the one shown in FIG. 5.

Another limitation associated with traditional PM machine geometriesrelates to flux saturation. In particular, due to overlapped phasewinding slots, the magnetically soft phase poles will saturate beforethe air gap can have a mean flux density equal to B_(r) of the permanentmagnets.

That is due to the reduced pole area remaining after sacrificing some toaccommodate the overlapped winding slots to form the three phases. FIG.6, shows a flux density of ˜2.1 Tesla in the phase pole that isenergized to couple with a PM in an attracting manner. The air gap peakflux density between the rotor PM and the energized phase poles at theirtips is ˜1.35 Tesla peak flux density, as shown in FIG. 7. The integralof the flux density across a pole would be much less than B_(r) for thepermanent magnet.

For example in the machine shown in FIG. 5, phase one has slots toaccommodate the phase two and three windings, segmenting what would be aphase one pole into 3 poles. If we look at only the phase one poles inthe machine in FIG. 5 with the winding slots for phases 2 and 3 removed,a phase one pole would be as shown in FIG. 9.

FIG. 10 illustrates magnetic flux for this device. FIG. 11 shows theflux density in the air gap over 360 degrees for phase one with thewinding slots for phases two and three removed and the same appliedcurrent as was used to create FIG. 7. Again, the 12 attracting phase onepoles can clearly be seen, and with the flux clearly at or around B_(r)over a much greater portion of the area of the pole face. The torqueproduced by the geometry used in FIG. 11 was 36 N-m compared to the 24N-m produced in FIG. 7, an increase of about 33%.

The above is not to suggest that the geometry shown in FIG. 9 representsa preferred PM machine geometry but rather to demonstrate that the lossof core material to winding slots for overlapped phases has asignificant effect on the amount of torque produced for the same appliedcurrent (i.e., the geometry in FIG. 9 could be implemented but itprobably would not be optimal). The conclusion that should be drawn fromthis is that a multiphase PM machine geometry that does not haveoverlapping phase windings would result in a higher power densitymachine.

Another limitation of traditional PM machine geometries relates to gapflux density. When the machine's phase coils are not energized, the gapdensity for aligned poles will be ˜½ the B_(r) of the permanent magnetif the phase coils are in series with the permanent magnets; whenenergized they would add to the field intensity [H] to increase the fluxdensity across the gap. The maximum possible gap flux density, since thepole face of the magnet is essentially the same area as the polescomprising a machine phase and both are in series with one another (foraligned poles), will be equal to B_(r) of the permanent magnet, or1.2-˜1.3 Tesla with neodymium magnets when the phase coil has currentflowing through it adding to [H].

Competitive attempts to increase the gap flux densities in permanentmagnet machines have been implemented that increase the pole face areaof the rotor permanent magnet to be greater than the pole area, thusallowing for higher air gap flux densities (areas A1+A2>A3 by 2:1, asshown in FIG. 12). This is done by placing more than one magnet in slotsin the rotor or alternately by shaping one magnet into a ‘U’ shape (notshown) directed toward a stator pole.

Such a solution for increasing the air gap flux density entailsproblems. The rotor would require a greater depth, thus adding weight,and would be more complicated since the magnets would need to be placedin the magnetically soft rotor iron. Thin structural metal at the endsof the permanent magnets to keep the poles of the permanent magnets fromshorting would result in a fragile rotor design. A PMC magnetic circuitprovides a solution for increasing the gap flux densities whilemitigating the problems associated with the above solution.

Notwithstanding the heavier, fragile and more complicated rotor, itstill does not address the loss of power density due to repelling fieldsand the small flux area on a stator pole due to overlapped phases.Therefore, even if this were a good solution for increasing the air gapflux density it does not provide a complete solution for overcoming someof the other limitations of the widely used three phase permanent magnetmotor geometry.

Another limitation associated with traditional PM machine geometriesrelates to current rise times. In particular, the exponential rise timefor the phase coils to obtain I_(max) is different when a phase coil isenergized to attract a permanent magnet than when repelling a permanentmagnet (as shown in the graph in FIG. 13). The data in this graph wascaptured using both an FEA analysis and from empirical data.

When energy is applied to a phase coil the expanding magnetic field isaided when the flux from the permanent magnet is in the same direction[attracting] as the expanding magnetic field of the phase coils andopposed when the flux from the permanent magnet opposes the expandingfield of the phase coils [repelling]. Therefore when the permanentmagnet flux is in the same direction as the expanding phase coil field,the current rise time is faster and when the permanent magnet flux is inthe opposite direction the current rise time is slower.

Torque versus speed in a rotating PM machine is a function of thecurrent through the Back Electromotive Force [BEMF]. The instantaneouscurrent is a function of the phase coil's resistance, inductance and theapplied voltage and BEMF over a given time interval or:

$\begin{matrix}{\mspace{79mu} {i = {\left( \frac{{Ea} - E_{bemf}}{R_{coil}} \right) \cdot \left( {1 - \xi - {\text{?} \cdot \frac{R_{coil}}{L_{coil}}}} \right)}}} & {{Equation}\mspace{14mu} 1} \\{{\text{?}\text{indicates text missing or illegible when filed}}\mspace{214mu}} & \;\end{matrix}$

The time interval is the time it takes for a rotor pole to sweep past astator pole. Torque is a function of the integration of [i] over thistime interval. Therefore, a faster current rise time has an impact onthe speed at which the rotating machine develops maximum power out. The[L] term is modified by the PM field orientation relative to thedirection the current is flowing in a phase coil. In the machine shownin FIG. 5, the phase coil's magnetic field orientation with respect tothe permanent magnet's field is equally distributed between opposing andaiding over time.

Therefore, the notion that a PM machine geometry containing onlyattracting (or aiding) fields would have superior performance in bothpower density and efficiency could easily be proved mathematically.

1. PMC Formulas & Principles

The voltage formula for one phase in a PMC machine is:

$\begin{matrix}{V_{in} = {{R \cdot I} + \frac{d\left( {\lambda \left( {\theta,i} \right)} \right)}{dt}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Lambda in the above equates to:

λ(θ,I)=L(θ)·i+K _(pm)(θ)  Equation 3

The K term, PM flux linkage, gives rise to the dominant torque in a PMCmachine, and also its speed voltage. L is constant within 2% over Thetain a PMC machine and is therefore independent of Theta. The torque thatcorresponds to the above is given in equation 4. Note that although L isconsidered to be independent of Theta, implying that the inductance termcould be stated simply as Li, for mathematical correctness dL (Theta,i)is used so as to account for any potential variation in L, no matter howsmall it may be.

$\begin{matrix}{{Torque} = {{\frac{1}{2} \cdot i^{2} \cdot \frac{{dL}\left( {\theta,i} \right)}{d\; \theta}} + {i\frac{{dK}_{m}(\theta)}{d\; \theta}} + {{Torque}_{cog}(\theta)}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

The model for one phase of the motor proper is a series resistor,inductor and voltage source, as depicted in FIG. 14.

Electrical energy that enters the machine can go to one of three places(in the absence of core losses). First, it can be lost as heat in thewindings; the winding resistance accounts for this. Second, it can bestored in the magnetic fields in the machine; the inductance accountsfor this. Finally, it can be converted to mechanical energy and sent outvia the shaft. It is the job of the BEMF voltage to account for this;the BEMF voltage times the current through it is the instantaneouselectrical power that is converted to instantaneous mechanical power andsent out via the shaft. The electrical equation of motion for a PMCmachine is:

$\begin{matrix}{V = {{Ri} + {L \cdot \frac{di}{dt}} + u}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Where v and i are the terminal voltage and current, respectively, u isthe BEMF, R is the winding resistance and L is the winding inductance.Multiplying the equation above by the current i results in:

$\begin{matrix}{{Vi} = {{Ri}^{2} + {\frac{d}{dt} \cdot \frac{1}{2} \cdot \left( {L \cdot i^{2}} \right)} + {ui}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

This is an energy conservation experiment that states that the power in(vi) goes either to heat (Ri²), stored magnetic energy (d/dt( . . . )),or into the BEMF, which represents the mechanical side of the machine.Thus ui is torque times speed, or mechanical power out. Finally, goingback to equation 1, note that if i=0, i.e., if the machine is opencircuit, then v=u, and so the measured terminal voltage at a speed thatrepresents the operational speed equals the BEMF for that particularspeed.

Since a PMC machine contains multiple phases, with multiple voltages,currents and flux linkages, one set for each phase must be considered.This is accomplished by creating appropriate vectors (V, I, Lambda, K)and matrices (R, L), and then by using the equations above. So, V, I andLambda become column vectors of the voltage across, the current through,and the flux linked by each phase. K then becomes a column vector of theflux linkage components due to the magnets, which is a function of rotorposition. R becomes a resistance matrix with resistances along thediagonal, and zeros off the diagonals. Finally, L becomes an inductancematrix with self inductances down the diagonal, and mutual inductanceson the off diagonals. Note that L will be a symmetric matrix since themutual inductance from one phase to another is the same as the reversemutual inductance, or, put mathematically, Lm,n=Ln,m.

FIG. 15 shows a section of the rotor and stator that comprise a ‘phasesection.’ A ‘phase section’ is the building block for a PMC machine. Thecomponents that comprise a ‘phase section’ consist of at least twostator poles on a stator segment placed adjacent and between two northpermanent magnet pole faces and a second stator segment with an equalnumber of poles placed adjacent and between two south permanent magnetpole faces. A coil is placed on each of the stator poles. A ‘singlephase section’ can be repeated more than once in a PMC design as will beapparent when looking at the geometries for two, three and six phase PMCmachines.

Both phase coils on the poles between two permanent magnet north poleswill always be energized with current in the same direction. The coilson the poles between two permanent magnet south poles will always beenergized with current in the opposite direction to the coils on thepoles between permanent magnet north poles. For example in the six phaseversion in FIG. 16 if coils ‘A and ‘C’ are energized and assuming thecoils are wound in the same direction about the poles, current willenter the start turn of coil ‘A’ and exit the start turn of coil ‘C.’Therefore, a unidirectional current is applied to all of the coils andits direction is determined by whether the coil resides between either anorth or south permanent magnet pole. The direction the unidirectionalcurrent flows through a coil is determined by the left hand rule andwould be where the coil's magnetic pole located on the magnet side formsa couple with the magnet. For example if a coil is located between theNorth permanent magnet poles the coil's magnetic pole facing thepermanent magnet would be energized to produce a South magnetic pole onthe magnet side and a North magnetic pole on the rotor side. The ‘A’ and‘C’ coils are ‘on’ when the ‘B’ and ‘D’ coils are off or vice versa oralternately energized. This would mean that only one of the two polesbetween permanent magnet North poles and only one of the two polesbetween permanent magnet South poles would be energized at any giventime but allowing for some overlap in the coil's ‘turn on’ and ‘turn offtiming. Some exceptions to the unidirectional current might beimplemented as shown in the example of FIG. 16, there is a firstunidirectional current in the coils ‘A” and ‘C’ and a secondunidirectional current in coils ‘B’ and ‘D’, where the secondunidirectional current flows in the opposite direction of the firstunidirectional current. In this case both coils between ‘like’ permanentmagnet poles are energized in opposite directions but with differentmagnitudes of current where one coil is energized to produce a fluxlinkage between the rotor and stator (normal current direction) and theother coil is energized only to the point to prevent a flux linkage orcouple between the rotor and stator (opposite to the normal currentdirection). Cases exist where bidirectional current can be used; suchcases are shown in FIGS. 20 & 21.

FIG. 16 shows a case where no phase coils are energized. The flux fromthe permanent magnets' north poles would traverse though the lowestreluctance path, through pole ‘B,’ through the rotor and then return tothe permanent magnets' south poles through pole ‘D,’ where the flux isillustrated as the blue region.

FIG. 17 shows how the flux from the permanent magnets adds and isdirected through a given set of stator poles by selectively energizingphase coils. Coils ‘A’ and ‘C’ are energized to produce the shownmagnetic polarities. The flux from the two permanent magnet north polescombine and traverse pole ‘A’ through the rotor and returns through pole‘C’ to the permanent magnets' south poles.

Since rotor poles are not aligned with poles ‘A’ and ‘C,’ a torque isproduced on the rotor that will act to align rotor poles with statorpoles ‘A’ and ‘C.’ It would be obvious that if viewed as a ‘single phasesection’ (as in FIG. 17) the rotor direction would not be predictable.This unpredictability is mitigated when placed in a phased relationshipwith other like ‘single phase sections.’

If the rotor is in an angular position where rotor poles are not inalignment with poles ‘B’ and ‘D’ and if the pole coils for poles ‘B’ and‘D’ were energized to have the magnetic polarities (as shown in FIG.18), a torque would be produced to bring the rotor poles in alignmentwith stator poles ‘B’ and ‘D.’

By adjusting the length of the permanent magnet pole faces ‘L1’ and ‘L2’in FIG. 19, the flux across a stator pole of length ‘L3’ can be adjustedto be equal to the air gap flux densities achievable in a field woundmachine. The PMC machine geometry is superior because it makes thatpossible without adding the copper weight and suffering additional I2Rlosses, as would be the case in a field wound machine.

In FIG. 20-A, phase coils ‘B’ and ‘D’ are energized only to the pointthat the flux through poles ‘B’ and ‘D’ is opposed and redirected topoles ‘A’ and ‘C.’ That would have a similar effect as shown in FIG. 17.The current flowing in the phase coils when opposing the permanentmagnet's flux would need to be controlled to prevent the production ofan opposing flux greater than the amount needed to be displaced. Intheory, phase coils ‘A’ and ‘C’ could be eliminated and coils ‘B’ and‘D’ could be fed a bidirectional current that either opposes orredirects the permanent magnets' flux to the proper poles. In FIG. 20-B,all of the phase coils are energized both to oppose and displace (‘B’and ‘D’) or to aid and redirect (‘A’ and ‘C’) the flux from thepermanent magnets.

The most compelling reason for using a bidirectional current in a phasecoil within a PMC machine is to dissipate any stored energy in a phasecoil at a ‘switch off event. The dissipation of the stored energy is themajor source of noise in a switched reluctance [SR] machine since abrief opposing torque is created when current is snubbed off just as arotor and stator pole come into alignment.

In a PMC machine, just prior to a rotor and stator pole coming into fullalignment (FIG. 21), the stored energy in phase coils ‘A’ and ‘C’ isdissipated in phase coils ‘B’ and ‘D.’ The returned stored energyflowing into coils ‘B’ and ‘D’ is in the same direction as the supplyand opposes the flux from the permanent magnets, which acts to maintainthe flux through poles ‘A’ and ‘C’ as the rotor moves into alignment.This allows the returned energy to be dissipated in a manner thatsupports rotation, thereby reducing the need for complex energy recoverycircuits as used in SR machines and allowing for quieter operation.

A PMC rotating machine can contain a wide variety of phases. QM Power ispresently focusing on two, three and six phase machines where a twophase machine provides a lower cost solution and a premium six phasemachine provides higher power density with extremely low torque ripple.The three phase PMC machine will serve the majority of marketapplications. These three offering types will allow a PMC machine to becost competitive with superior performance in a cost driven market orprovide superior performance in a performance driven market.

A PMC two phase machine geometry is shown in FIG. 22 and, as can beseen, it is made up of ‘phase sections’ as depicted in FIGS. 15 through18. In the PMC two phase machine every other ‘phase section’ is offsetby 90 electrical degrees. PH1 and PH1′ can be thought of as mirrorimages of each other because as PH1 poles ‘A’ and ‘B’ leave alignment,poles ‘C’ and ‘D’ approach alignment; as that happens in PH1, theopposite is happening with PH1′ because poles ‘A’ and ‘B’ would beapproaching alignment while PH1′ poles ‘C’ and ‘D’ would be leavingalignment. This same relationship exists between the poles of PH2 andPH2′. Four ‘phase sections’ make up phase 1 and its complement phase andfour ‘phase sections’ make up phase 2 and phase 2′. A timing sequence isshown in FIG. 23. A three phase PMC machine is shown in FIG. 24 alongwith its timing sequence in FIG. 25. A six phase PMC machine is shown inFIG. 26 along with its timing sequence in Figure.

As with an SR machine, a PMC machine does not have a steady-stateequivalent circuit as compared to AC and DC machines as a result of thenon-linear characteristics as suggested by equation 3. A PMC machine hasthe following features:

-   -   1) A PMC machine has unidirectional current producing        unidirectional torque as opposed to AC machines and all DC        machines, except those in the SR motor class. Since only one        switch is required to control current in a phase this reduces        the number of power converter switches and makes the drive more        economical. There is no shoot through failure mode since a phase        switch only faces one side of the power source.    -   2) The torque constant is given by the slope of the PM flux vs.        rotor position and L (Theta,i) making it non-linear and thus        impossible to derive a simple equivalent circuit.    -   3) A PMC motor has high starting torque like a series DC motor,        the workhorse for traction applications. A PMC motor, however,        would be lighter and more efficient than a series motor given        that the field wound coils are replaced with permanent magnets.    -   4) Permanent magnet flux varies with rotor position and thereby        allows for comparably higher performance generating action,        another attractive characteristic for automotive applications.    -   5) The direction of rotation is easily controlled by changing        the phase excitation sequence.    -   6) Features 1, 4 and 5 make the use of a four quadrant        controller possible.    -   7) Torque and speed are controlled by altering the phase        excitation voltage.    -   8) Current PMC designs do not operate directly from a three        phase line supply without a power converter. In order to be cost        competitive with lower cost fixed speed induction motors, a        synchronous squirrel cage PMC motor is being developed.    -   9) Due to the reduction of power switches in the converter and        simplified rotor design, a PMC machine will provide superior        performance over other PM motors at a lower cost.    -   10) Since rotor position can be accurately controlled a PMC        machine is also suitable for precision high performance        servo-motor applications.    -   11) All of the phases in a PMC machine are ‘electrically        independent’ therefore a fault in one phase has no effect on the        other operational phases. A fault in a single phase in almost        all other phased motors types, with the exception of an SR        motor, has catastrophic implications. This feature is especially        beneficial for machines used in ‘high risk’ applications such as        motors, generators and actuators used for aerospace, defense,        medical, nuclear, traction and electric vehicles, chemical        handling, etc.    -   12) The performance due to the loss of a phase, in a multiphase        machine, is diminished as a function of the number of machine        phases. As the number of phases increases the impact on        performance from the loss of any one phase is reduced. A PMC        machine can be easily configured to virtually any number of        phases for both motors and generators.    -   13) No repelling fields are used, thus negating the associated        losses and power density reduction associated with their use; it        also allows for faster current rise times for producing higher        torque at higher speeds.    -   14) With a PMC geometry, where the magnets are placed on the        stator, the ratios of the total magnet length to the length of a        pole face is such that high gap densities can be achieved in a        light weight and low loss PM configuration. The high gap flux        densities increase the PMC machine's power density when        operating as a motor or as a generator.    -   15) A PMC machine does not use cross rotor flux linkages, nor        does the rotor serve as PM ‘back iron’ as with other PM        machines. The resulting significant reduction in the rotor and        overall machine weight is a beneficial feature for many        applications and can be particularly important for improving the        performance of larger machines, including wind turbine        generators.    -   16) A PMC machine has no attached components on the rotor, i.e.,        permanent magnets. This feature allows for holding a smaller and        more consistent air gap length, increases reliability and allows        the machine to operate at much higher rotational speeds when        operated as a motor or generator.    -   17) The PMC geometry is equally applicable to non-rotary        applications such as actuators, linear motors, linear        generators, high power latches, etc.    -   18) A PMC machine's phases are geometrically independent and do        not rely upon overlapped phase poles. This feature not only        increases the effective pole areas, it additionally isolates the        phases from mutual inductance.

Finding reliable and complete competitive variable speed motor data ischallenging, particularly for smaller scale devices, where efficiencytends to be lower. Most motor manufacturers only publish what they wanta prospective customer to see or only the highest performance range on aparticular motor's operating curve.

One of the most common misconceptions in the scientific and engineeringcommunity is that ‘motors already operate in the 90 plus percentefficiency range’ when in fact motors have a wide range of efficienciesnot just one efficiency. Efficiency is determined by many factors,including what RPM output level the motor is operating at within itscapacity range, by the controlling methods employed, by the powerdensity (weight) of the motor, and whether or not any active cooling isused; a full understanding of these factors is required to evaluate theintrinsic technical value proposition of the machine. Since few of thesemetrics, other than individual peak efficiencies and weights aretypically provided in manufacturers' product specifications, it is oftendifficult to determine which option represents the best choice for anapplication. The analysis below focuses on the physics that define aparticular motor geometry and examines the relationship between motorsize, output level and efficiency.

To begin, it is important to understand that efficiency normallyimproves as a rotating electrical machine increases in diameter sincethe flux path length tends to scale linearly with size. So, for a givenflux density, and hence shear stress, the amp-turns must scale linearlytoo. At the same time the winding cross section is increasingquadratically, and so the Ohmic loss is unchanged. On the other hand,the torque out (and power for a fixed speed) is growing quadratically atconstant rotational speed, or at least linearly with constant tip speed.Thus, efficiency improves because output goes up while losses stay thesame, all at a constant flux density.

All motors will have both high and low efficiencies over their fulloperating range and at ‘no-load’ and ‘stall’ efficiency will even bezero. If a competitive motor curve only shows high efficiencies they areeither not showing the entire operating range of the underlying motor orthey are using controlling methods on an oversized motor, so that thedevice can run at a lower power than the machine is capable of, but at ahigher point on its intrinsic efficiency curve.

The left side of FIG. 28 illustrates the uncontrolled speed-torque andefficiency curves for conventional PM motors which have an intrinsicallylinear speed-torque relationship. Since ‘peak power’ and ‘peakefficiency’ do not occur at the same point on the uncontrolled operatingcurve for the most widely used PM motor geometries, the challenge formotor designers was to find a way to obtain the high efficiency foundnear it's no load speed (i.e., at the maximum point of its efficiencycurve) at a power output level that commercial applications require.While a fixed commutation (i.e., uncontrolled) PM motor is shown in theleft graph of FIG. 28, the right side shows the same motor usingcontrollers to limit ‘power in’ and ‘power out.’ FIG. 30 illustratestorque and power output as a function of RPMs. FIG. 31 illustratestorque as a function of RPMs.

The conventional solution has been to use a motor that is large enoughto operate at the targeted application's power specifications withoutexceeding the higher intrinsic high efficiency range, and then usingelectronic control to limit the power output to operate in that range.However, as can be seen in the right side of FIG. 28, in order toachieve such high operational efficiency, the motor would have to have apeak power capacity between 30-50% greater than the actual range it isdesigned to be run at in the particular application. To obtain such ahigher peak power, the motor has to be larger (oversized), thusincreasing the weight of the machine. Since the cost of a motor istypically dominated by the steel and copper raw materials (i.e., theweight) and the control electronics (if needed) the costs of fabricatingsuch conventional PM motors are necessarily higher than they would befor a motor with intrinsically higher efficiency over a wider range ofuncontrolled operating speeds; such a motor would not need to beoversized since its peak output power would be near its peak efficiency.Again, a motor with those attributes would not need to be oversized, andwould potentially eliminate (or at least minimize) the controllercomponents, and would, therefore, lead to lighter and cheaper to build(and sell) alternatives offering the same power.

The design of the invention is the first commercially available motorthat doesn't need to be oversized to meet the efficiencies demanded bythe motor marketplace. The invention obtains its cost advantages byhaving an intrinsic hyperbolic uncontrolled speed-torque curve, whichleads to an almost rectangular efficiency curve. For the disclosedmotor, the no load and stall efficiencies are still zero but theyquickly climb above 90% and hold across the operating range of speeds ofthe device (see FIG. 32 below)—an especially important quality forvariable speed applications. The disclosed motor allows one to obtainpeak power at or near the machine's intrinsic peak efficiency. While theweight of a motor is not linear to the power output, the intrinsic peakefficiency of the linear speed torque curve of an uncontrolledconventional PM motor occurs at a point that is approximately 27% lowerthan that of its peak power.

FIG. 29 is a comparison of the expected power density, efficiency andspeed benefits of the QM Power alternative compared to market leadingalternatives for variable speed automotive applications.

Importantly, there are no known manufacturing or materials limitationswith a PMC Machine that prevent rapid commercialization. Aside from theautomotive market, the prospect of a motor with smaller size and lowerweight, but with the same or higher efficiencies and output speeds, is asignificant value proposition for a variety of applications.

FIG. 31 is the speed vs. torque curve for a fixed commutation 6 phase 1HP machine with PMC geometry. Efficiency remained above 90% for over 50%of the range. Due to their linear speed torque curve, incumbent 1 HPmachine alternatives that produce 1 HP at values above 90% efficiencywith fixed commutation will only remain above 90% efficient for ˜15% oftheir operating range, as illustrated in the left hand graph of FIG. 32.Efficiencies above 90% occur in this graph only from where theefficiency curve crosses the torque curve on the left side of the graphto the first dotted vertical line on the left side of the graph.

As suggested by the PMC motor equations presented earlier, speed andtorque scale proportionally for a PMC motor based upon input voltage.The input voltage was held constant during the testing, thereforeconstant power was produced at 1HP for the above graphs. The Opera-RManalysis results of a 10 KW PMC motor are shown in FIGS. 33 and 34. FIG.33 shows a speed vs. torque and power out for a 10 KW motor and FIG. 34shows speed vs. torque and efficiency. Using curve fitting on the speedvs. torque for 1 KW, 10 KW and 50 KW motors we found that torque is afunction of speed to the power of −0.98 for all cases, indicating thatscaling is indeed quadratic. An Opera RM FEA analysis of the disclosedtechnology suggested that a continuous 50 KW motor with a peak torque of200 N-m could be developed with a proposed motor diameter of 250 mm, alength of 150 mm with a weight of approximately 32 Kg —all within thegiven acceptable parameters.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that specificdetails are not required in order to practice the invention. Thus, theforegoing descriptions of specific embodiments of the invention arepresented for purposes of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formsdisclosed; obviously, many modifications and variations are possible inview of the above teachings. The embodiments were chosen and describedin order to best explain the principles of the invention and itspractical applications, they thereby enable others skilled in the art tobest utilize the invention and various embodiments with variousmodifications as are suited to the particular use contemplated. It isintended that the following claims and their equivalents define thescope of the invention.

1. A method comprising: in a machine comprising a rotor without magnetsand a stator comprising a plurality of phase sections, each phasesection corresponding to one of a plurality of electrically independentphases of the machine and each phase section having pairs of pole facesof permanent magnets arranged with same facing magnetic poles in which amagnetic pole of a permanent magnet faces a same magnetic pole ofanother permanent magnet, the pairs of pole faces comprising two northsame facing permanent magnet pole faces and two south same facingpermanent magnet pole faces, the stator further comprising two statorpoles between the two north same facing permanent magnet pole faces andtwo other stator poles between the two south same facing permanentmagnet pole faces, and a winding on each of the stator poles, energizingthe windings on the two stator poles with current in a same firstdirection and energizing the windings on the two other stator poles withcurrent in a same second direction opposite the same first direction. 2.The method of claim 1 wherein: each winding has a side facing one of thepermanent magnets and another side facing the rotor; and the methodfurther comprises energizing first windings between the two north samefacing permanent magnet pole faces to cause each first winding to have asouth magnetic pole on the permanent magnet side and a north magneticpole on the rotor side.
 3. The method of claim 1 wherein: the two statorpoles between the two north same facing permanent magnet pole facescomprise first and second stator poles; the other two stator polesbetween the two south facing permanent magnet pole faces comprise thirdand fourth stator poles; the first stator pole has a first winding woundabout the first stator pole, the second stator pole has a second windingwound about the second stator pole, the third stator pole has a thirdwinding wound about the third stator pole, and the fourth stator polehas a fourth winding wound about the fourth stator pole; the first andthird windings are wound in a same first direction; the second andfourth windings are wound in a same second direction; and the methodfurther comprises: energizing the first and third windings with a firstcurrent in a same first direction; and energizing the second and fourthwindings with a second current in a same second direction opposite thesame first direction.
 4. The method of claim 3 further comprising:energizing the first and third windings with the first current in thesame first direction while not energizing the second and fourthwindings; and energizing the second and fourth windings with the secondcurrent in the same second direction opposite the same first directionwhile not energizing the first and third windings.
 5. The method ofclaim 3 further comprising energizing the first and third windings witha first magnitude of current and energizing the second and fourthwindings with a second magnitude of current, wherein the first magnitudeof current is different than the second magnitude of current.
 6. Themethod of claim 5 further comprising energizing the first and thirdwindings with a first unidirectional current having a first magnitude ofcurrent and energizing the second and fourth windings with a secondunidirectional current having a second magnitude of current, wherein:the second unidirectional current flows in a direction opposite of thefirst unidirectional current; the first magnitude of current energizesat least one of the first and third windings to produce a flux linkagebetween the rotor and the stator; and the second magnitude of currentenergizes at least one of the second and fourth windings to prevent theflux linkage between the rotor and the stator.
 7. The method of claim 3further comprising dissipating energy stored in the first and thirdwindings prior to a rotor pole and one of the stator poles coming intofull alignment.
 8. The method of claim 3 further comprising dissipatingenergy stored in the first and third windings prior to a rotor pole andone of the stator poles coming into full alignment and cause thedissipating energy to flow into the second and fourth windings andmaintain flux through the first and second windings as the rotor poleand the one of the stator poles move into full alignment.
 9. The methodof claim 3 wherein the first current enters a first start turn of thefirst winding and exits a second start turn of the third winding, andthe second current enters a third start turn of the second winding andexits a fourth start turn of the fourth winding.
 10. The method of claim9 wherein the first current causes magnetic flux from the north samefacing permanent magnet pole faces to traverse from the first windingthrough the rotor and through the third winding to the south same facingpermanent magnet pole faces.
 11. The method of claim 9 wherein thesecond current causes magnetic flux from the south same facing permanentmagnet pole faces to traverse from the fourth winding through the rotorand through the second winding to the north same facing permanent magnetpole faces.
 12. The method of claim 1 further comprising changingdirection of rotation of the rotor by changing a sequence of energizingthe windings.
 13. The method of claim 1 further comprising controllingtorque by altering a voltage used for energizing the windings.
 14. Themethod of claim 1 further comprising controlling speed by altering avoltage used for energizing the windings.
 15. The method of claim 1further comprising selecting the machine as at least one of a two phasemachine, a three phase machine, and a six phase machine.
 16. The methodof claim 1 further comprising selecting the machine as at least one of atwo phase motor, a three phase motor, and a six phase motor.
 17. Themethod of claim 1 wherein the machine produces unidirectional torque.18. A method comprising: in a machine comprising a rotor without magnetsand a stator comprising a plurality of phase sections, each phasesection corresponding to one of a plurality of electrically independentphases of the machine and each phase section having a plurality of northpermanent magnet pole faces arranged with north same facing magneticpoles, a plurality of south permanent magnet pole faces arranged withsouth same facing magnetic poles, a first plurality of stator polesbetween the north permanent magnet pole faces, a second plurality ofstator poles between the south permanent magnet pole faces, and awinding on each of the stator poles, wherein same facing magnetic polesare a magnetic pole of a permanent magnet facing a same magnetic pole ofanother permanent magnet, energizing the windings on the first pluralityof stator poles with current in a same first direction and energizingthe windings on the second plurality of stator poles with current in asame second direction opposite the same first direction.
 19. The methodof claim 18 wherein: each winding has a side facing one of the permanentmagnets and another side facing the rotor; and the method furthercomprises energizing first windings between the two north same facingpermanent magnet pole faces to cause each first winding to have a southmagnetic pole on the permanent magnet side and a north magnetic pole onthe rotor side.
 20. The method of claim 18 further comprising changingdirection of rotation of the rotor by changing a sequence of energizingthe windings.
 21. The method of claim 18 further comprising controllingtorque by altering a voltage used for energizing the windings.
 22. Themethod of claim 18 further comprising controlling speed by altering avoltage used for energizing the windings.